Question

Compared to the salient-pole Hydroelectric generators, the steam and the gas-turbine generators have cylindrical rotors for
1. Better air-circulation in the machine
2. Reducing the eddy-current losses in the rotor
3. Accommodating larger number of terms in the field winding
4. Providing higher mechanical strength against the centrifugal stress

Answer 1

Correct Answer - Option 4 : Providing higher mechanical strength against the centrifugal stress

Non-Salient pole generator (the steam and gas turbine) has cylindrical rotors that have a very high speed of rotation. Therefore, a cylindrical rotor provides greater mechanical strength and have more accurate dynamic balancing.

The differences between the salient pole rotor and the cylindrical rotor are shown below.

Salient pole rotor	Cylindrical rotor
Large diameter and short axial length	Small diameter and long axial length
used for low-speed alternators	Used for high-speed turbo-alternators
Has  projecting poles	Has no projecting poles
Needs damper windings	Do not need damper windings
Windage loss is more	Windage loss is less